Process of producing aliphatic dinitrile from fatty acids



July 28, 1964 HAJlME MIHARA ETAL 3,142,596

PROCESS OF PRODUCING ALIPHATIC DINITRILE FROM FATTY ACIDS Filed Dec. 10, 1959 2 sheets-sheen FIG.1

FIG.2

INVENTORS' Hajime Mih ara Ich|ro Mlwa K| sabu ro Ueno 3y Klyoshl Osawa $M7r Mm ATTORNEY 3,142,696 PROCESS OF PRODUCING ALIPHATIC DINITRILE FROM FATTY ACIDS Filed Deg. 10, 1959 J y 1964 HAJlME MIHARA ETAL 2 Sheets-Sheet 2 INVENTORS Ha'ime Mihara chiro Miwa Kisaburo Ueno BY Kiyoshi Osawa filampnwclwg, Rudy-045'" ATTORNEYS United States Patent 3,142,696 PRGCESS 0F PRODUCING ALIPHATIC DINITRILE FRSM FATTY ACIDS Hajime Mihara, leliiro Miwa, Kisaburo Ueno, and Kiyoshi Osawa, all of Toyonuma, Sunagawa, Japan, assignors to Toyo Koatsu Industries, Incorporated, Tokyo, Japan, a corporation of Japan Filed Dec. 10, 1959, Ser. No. 858,660 Claims priority, application Japan Apr. 20, 1959 4 Claims. (Cl. 260-4652) The present invention relates generally to an improved chemical process and it relates more particularly to an improved method for the production of aliphatic dinitrile compounds from the corresponding aliphatic dibasic acids.

The methods heretofore employed and proposed in the production of aliphatic dinitrile compounds have been characterized by their inefiiciency, low yield, and other disadvantages and drawbacks. Thus, in accordance with the method of US. Patent No. 2,132,849 (1938) an aliphatic diamide or an aliphatic dibasic acid such as sebacic acid or adipic acid is reacted in the liquid phase with an excess of ammonia gas in the presence of ammonium molybdate as a catalyst. The yield is very low, from 32% to 50.5%. According to German patent No. 734,558 (1943) adipic acid and ammonia gas are reacted in the presence of 2% to 3% of a phosphoric acid. A yield of 80% to 84% adiponitrile is claimed although in actuality the overall yield is considerably less by reason of the high amounts of polymer formed.

The use of a silica gel catalyst in a vapor phase reaction has only produced a yield of 70% aliphatic dinitrile and while the use of a boric phosphate catalyst is said to have increased the yield somewhat this has only been on a laboratory scale with a very short catalyst life. Other processes and methods have been proposed for the production of aliphatic dinitriles but these have also left much to be desired.

It is thus a principal object of the present invention to provide an improved method for the production of aliphatic dinitrile compounds.

Another object of the present invention is to provide an improved method of producing aliphatic dinitriles from the corresponding aliphatic dibasic acids.

Still another object of the present invention is to provide an improved method of the above nature characterized by its efficiency, high yield and low polymer formation.

The above and other objects of the present invention will become apparent form a reading of the following description taken in conjunction with the accompanying drawing wherein,

FIGURES l and 2 are diagrammatic views of experimental apparatus for determining operating parameters of the present process; and

FIGURE '3 is a flow diagram of an apparatus and method embodying the present invention.

In a sense the present invention contemplates the improved method of producing an aliphatic dinitrile compound from the corresponding aliphatic dibasic acid and comprising the steps of introducing said aliphatic dibasic acid into a vaporizing zone at a temperature at least equal to the vaporization temperature of said dibasic acid to vaporize a part of said dibasic acid and leave a part thereof in an unvaporized state, reacting said dibasic acid vapors with ammonia to produce said dinitrile compound, removing said unvaporized dibasic acid from said vaporizing zone, cooling said removed dibasic acid and returning it to said vaporizing zone. The reaction between the ammonia and aliphatic dibasic acid vapors are advantageously effected in the presence of a catalyst selected from the class consisting of the combination of molybdic 3,142,696 Patented July 28, 1964 ice acid and phosphoric acid and/ or vanadic acid and phosphoric acid. Furthermore, the aliphatic dibasic acid, preferably a normally solid aliphatic dibasic acid is first heated to melt and the same is introduced into the vaporizing zone in a liquid state, the unvaporized aliphatic dibasic acid from the vaporizing zone being recycled through the melter.

It has been found that when the unvaporized aliphatic dibasic acid is permitted to remain in the vaporizing zone at close to the elevated temperature thereof, there is a modification of the aliphatic dibasic acid as evidenced by a decrease in the carboxyl radical. This occurrence is detrimental to the aliphatic dinitrile production and has been overcome by the present process.

The relationships between the complete vaporization time of azelaic acid when subjected to a stream of hot ammonia gas, the velocity of the ammonia gas and the reaction temperature were determined by use of the apparatus illustrated in FIGURE 1 of the drawing and are shown in the following Table I. The apparatus includes a vaporization chamber 4 provided at its upper part with an introducing conduit 6 having a gate cock 3.

Communicating with the lower part of the chamber 4 is an ammonia inlet conduit 7 provided with an enlarged section 8 surrounded by a suitable heating element 9. Located in the chamber 4 directly above the ammonia inlet is a charge carrying screen 10 above which is an ammonia outlet pipe 11. The chamber 4 is surrounded by a heater 12 and'tempe'rat'ure 'within the chamber 4 is determined by a suitable thermometer nested in a well 13 entering the bottom part of the chamber 4.

In use, a small open receptacle 14 carrying 0.03 gram of azelaic acid is deposited on the screen 10 by dropping it in the chamber 4 through the open gate cock 3 which is thereafter closed. Ammonia is then circulated through the chamber 4 at various velocities and temperatures in the vaporizing zone of the azelaic acid charge. The times required for initiating the melting, initiating the vaporiz ing, completing the melting and completing the vaporizing of the azelaic acid were measured in seconds and the linear velocity of the ammonia in centimeters per second.

TABLE I Time Required for Total Vaporization of Azelaic Acid Linear velocity of ammonia emJsec. Temp.

Sec. Sec. Sec. Sec. 150. 0 114.0 105.0 108.0 g 77.0 88.0 76.0 75.0 66.0 68.0 66.0 57.0 51.0 65. 0 58.0 55. 0 41. 0 44. 0 42. 0 49.0

It was observed from the above tests that between the initiation and completion of the melting there was a partial vaporization of the azelaic acid. At the temperatures of 330 C. and 345 C. the rate of vaporization is sharply diminished, requiring in excess of about secends to eifect complete vaporization. It may be postulated from this that the azelaic acid changes in composition or otherwise becomes more difficult to vaporize. Further, at a temperature of 360 C. complete vaporization was effected in 57 to 89 seconds, at 380 C. in 50 to 65 seconds and at 400 C. in 41 to 53 seconds and in no case was any dark brown residue observed after the vaporization of the azelaic acid. It is also important to note that at ammonia velocities between 20 and 83.8 cm./sec. there was little variation in the time required for total vaporization.

Tests were also made in connection with the modification of azelaic acid and adipic acid with heat as measured by the change in the carboxyl radical content thereof. The apparatus employed was that illustrated in FIGURE 2 of the drawing which difiered from that previously described only in that the charge receptacle 17 was in the form of a glass cup, 9 mm. in diameter and 12 mm. high and was suspended above the screen 10. The charge consisted of 0.58 gram of azelaic or adipic acid placed in the receptacle 17 and the ammonia velocity was 20 cm./sec. and the temperature was 330 C. The heat treating time was varied. It required from 36 to 56 seconds from the initiation of melting to the completion thereof and from 425 to 436 seconds from the initiation of melting to a discontinuity or tentative halt in vaporization at which point a surface coloration was observed. Vaporization from the surface resumed after the interval of discontinuity and an additional 110 seconds was required for the vaporization to terminate. The material that was treated for 425 to 436 seconds produced a residue with a 23% change in the carboxyl radical content. The rates of change of the residual carboxyl radical of azelaic acid and adipic acid for different times are shown in Table II.

TABLE II Rate of Change of Azelaic Acid and Adz'pic Acid Sec. Azelaic acid,

percent Adipic acid, percent It was thus determined by the above that subjecting aliphatic dibasic acids to elevated temperatures for extended periods effects an increase in the molecular weight of the material thereby reducing its usefulness in the production of the aliphatic dinitriles whereas a rapid vaporization of the aliphatic dibasic acid effected little chemical change thereof. Moreover, as a practical matter, it is almost impossible to completely instantaneously vaporize the dibasic acids in large scale apparatus by conventional methods.

It was observed that aliphatic dibasic acid which accumulated in the bottom of the ammonia containing vaporizing zone after a lapse of time converted to a polymer-containing nitrogen. For example, after a 30 minute interval a pitchlike material was drawn from the lower section of the vaporizing zone, turning into a black polymeric mass containing 6.9% to 9.0% nitrogen and having a residual carboxyl radical of 3.8 to 4.7 x mol./gr., equivalent to a value of 35.8% to 44.5% in terms of azelaic acid. Where the polymeric material accumulated and remained in the vaporizing zone during 1000 hour operation it became a low oxygen-containing glossy dry pitch of the following composition:

H, percent N, percent 0, percent 0, percent Thus, by promptly removing the unvaporized carboxylcontaining material from the vaporizing zone, cooling the material and recycling it through the vaporizing zone, the useful life .of the vaporizing zone was considerably increased and the accumulation of the undesirable polymeric material therein was very low.

It was further found that by passing the ammonia and vaporized aliphatic dibasic acid emerging from the vaporizing zone into contact with certain preselected catalysts, a very high conversion efficiency resulting in an aliphatic dinitrile yield exceeding 90% could be achieved. These catalysts are highly economical and may be prepared by adding up to several percent of molybdic acid or vanadic acid and phosphoric acid to silica gel together with a suitable alkalizing agent such as potassium hydroxide in an amount sufficient to maintain the pH of the mixture no higher than 7. The above materials are adsorbed by the silica gel or if desired, water may be added and then it may be mixed with an active earth and molded and finished in the manner well known in the art.

Referring now to FIGURE 3 of the drawings which diagrammatically illustrates an apparatus and flow diagram by which the present process may be practiced, the reference numeral 20 generally designates any suitable melter for the aliphatic dibasic acid being processed, the aliphatic dibasic acid being introduced through a feed opening. The molten aliphatic dibasic acid is withdrawn from the melter 20 and delivered by a pump 21 and piping into the top of a vaporizing tower 22 where it is distributed in droplet form as a spray. The tower 22 is packed in the vaporizing zone 23 with a suitable material such as Raschig rings. Also introduced into the top of the tower 22 is ammonia, preheated as will be hereinafter set forth, and the mixture of ammonia and vaporized aliphatic dibasic acid is discharged from the bottom of the tower 22 and fed to the bottom of a reaction tower 24. The unvaporized aliphatic dibasic acid flows to the bottom of tower 22 and passes by Way of jacketed cooling pipes 26 and pump 27 back to the melter 20 for recycling, having been cooled to a temperature preferably not exceeding 200' C.

The reaction tower 24 is packed with a catalyst carried on a suitable carrier as above set forth so that the aliphatic dibasic acid is completely dinitrilized as it passes upwardly with the ammonia in contact with the catalyst. The gases leaving the tower pass through a heat exchanger 28 to cool the gases which are then fed to a separation tower 29 where the aliphatic dinitrile condenses. The unreacted ammonia flows from the top of the tower 29 and is delivered by a blower 30 and suitable conduits by way of the heat exchanger 28 where the ammonia temperature is raised in cooling the reaction gases to a heating unit 32. The temperature of the ammonia is further raised by the unit 32 to a temperature preferably between 400 C. and 420 C., the hot ammonia being fed to the vaporizing tower 22 as aforesaid. Additional ammonia is introduced into the system at point 53 following the tower 29 to replace the ammonia consumed in the process. Under normal operating conditions the temperature in the vaporizing zone 23, reaction tower 24 and the piping between the towers 23 and 24 is 320 C. to 350 C., and in piping 26, gear pump 27 and melter 20, pump 21 and aliphatic dibasic acid inlet to tower 22, to 220 C. It is important to note that the vaporizing tower 22 and the catalyst reaction tower 24 are separated to great advantage, since if they were combined the catalyst would be coated by the pitchlike material evolved from the unvaporized aliphatic dibasic acid, greatly reducing the catalyst life to a duration of one week at most. Furthermore, if the unvaporized aliphatic dibasic acid were not handled in accordance with the present process, the resistance to flow through the tower 22 would be greatly increased in a short time by reason of the accumulation of the pitchlike material on the walls and backing. In the aforesaid case the useful life of the tower 22 would also be less than a week.

The following examples are merely given by way of iilustrations of the process of the present invention:

EXAMPLE 1 The catalyst was prepared by dissolving 14 parts potassium hydroxide and 8.94 parts of ammonium metavanadate in warm water, the solution being heated with the evolution of ammonia. 23.4 parts of phosphoric acid (purity of 89%) and sufficient water were then added to make 1000 parts. The ratio in the solution of K20 1 P205 I V205 was 2.72% :3.0%:l.0% and the pH of the solution was 3.1. A basket containing 100 parts of silica gel screened to mesh or more was immersed in the solution for 30 minutes, then removed, dried and heat-treated at 350 C. for four hours to complete the supported catalyst. The ratio of phosphoric acid to vanadic acid was 3:1 and the inorganic salts contained in the silica gel was approximately 6.0%.

Azelonitrile (heptamethylene-dinitrile) was produced in the apparatus described above wherein the vaporizing tower 22 had an inner diameter of 200 mm. and was 2.5 m. high and packed with 25 mm. Raschig rings and the reaction tower 24 had an inner diameter of 200 mm. and a height of 3 m. and contained 30 kg. of the catalyst pre pared as above and was heated at 350 C. by means of circulating Dowtherm through a jacket surrounding the tower 24. Ammonia preheated by the heating unit 32 to a temperature of 420 C. is blown into the top of the vaporizing tower 22 at the rate of 190 liters/ min. (N.T.P.) and the molten azelaic acid is pumped into the tower 22 at the rate of 3.2 kg./hr. Approximately 80% to 85% of the azelaic acid vaporizes and is delivered with the ammonia to the reaction tower 24 where the mixture rises in contact with the catalyst to convert the azelaic acid via the acid amide to azelaic dinitrile. The dinitrile admixed with aqua ammonia is cooled in passing through the heat exchanger 28 to condense a mixture of aqua ammonia and dinitrile which accumulates at the bottom of the separation tower 29; the unreacted ammonia and added ammonia being blown through the heat exchanger 28 to heat the same and thence through the preheater unit 32 to the tower 22. After about 4 hours of continuous operation the reaction product accumulating in the tower 29 is removed and is separated into two layers by the addition of benzene. The benzene layer is distilled off under reduced pressure of 13 mm. Hg, a small fraction boiling off at 67 C. to 98 C. and the major part, azelonitrile, distilling off at 134 C. to 135 C. under a pres sure of 1.5 mm. Hg to leave a small residue. The azelaic acid unvaporized in the tower 22 is cooled to 150 C. and returned to the melter 20 thereby achieving a maximum vaporization yield of efiiciency of the azelaic acid with a minimum of undesirable conversion thereof.

The four hour yield contained 3.0 to 4.0% of low boiling point material and 89.5 to 92.0% of azelonitrile. The low boiling point material was fractionally distilled at 13 mm. Hg pressure and resulted in a 21% fraction at 67 to 69 C., mainly cyclooctanone; a 73% fraction at 80 to 83 C., mainly capronitrile; and a 6% fraction at over 98 C., mainly azelonitrile.

When adipic acid was employed instead of azelaic acid and the operating conditions were modified so that the adipic acid at 30 kg./ hr. and ammonia at 300 l./ hr. where fed to the vaporizing tower 22 and the temperature of the melter 20 and the material in piping 26 was 180 C., the yield of adiponitrile was 91.0%.

EXAMPLE :2

The catalyst is produced by adding to 200 parts of water 4 parts of ammonium metavanadate and then 37.6 parts of potassium hydroxide and heating the solution with the evolution of ammonia, 52 parts of phosphoric acid (89% purity) and sufficient water to make 1000 parts are then added. The proportion of K O:P O :V O was 2.l:2.2:0.15 and the pH of the solution was 5.95 at 25 C. As in Example 1, 100 parts of silica gel are immersed in the above solution for 30 minutes, then removed, dried and heat-treated at 300 C. for 4 hours to produce a catalyst having a small proportion of vanadic acid relative to the phosphoric acid. The amount of inorganic salts adsorbed by the silica gel is approximately 9% of the silica gel.

30 kg. of the above catalyst was substituted for the catalyst of Example 1 and azelaic acid was treated in the same manner as Example 1 under the same operating conditions. The yield of pure azelonitrile after 8 hours continuous operating averaged 90% and this yield did not decrease even after 1500 hours of continuous operation.

EXAMPLE 3 The catalyst was prepared by dissolving 15 parts of ammonium molybdate and 37.6 parts of potassium hydroxide in 500 parts of water and heating the solution with the evolution of ammonia. 46.3 parts of 89% phosphoric acid and enough water are added to make 1200 parts, the solution'having a pH of 5.9 at 21 C. and a ratio of MoO :P O :K O of 0.8:2.0:l.7. 100 parts of silica gel is immersed in the solution and treated as in Example 1. 30 kg. of the catalyst was substituted for that of Example 1 and employing the same operating conditions and rates the yield of the azelonitrile from azelaic acid was 92.0%

EXAMPLE 4 The catalyst was formed by dissolving 3.2 parts silica gel powder of to 110 mesh in a solution of 2 parts of potassium hydroxide in 100 parts of water and ammonium molybdate (assay minimum 81.0% M00 is added as in Example 3. With the solution which has been boiled with the evolution of ammonia and having a pH of 7 is mixed 96.8 parts of the above silica gel powder and well kneaded. 5 parts diatomaceous earth, 5 parts kaolin and a small amount of water is then added and kneaded to form a moldable mass. The resulting mass is then formed into cylinders 6 mm. in diameter and 6 mm. high which are dried and heated at 350 C. The breaking strength of the resulting catalyst was 28 to 42 kg./cm.

Employing the same operating conditions and rates of Example 1 except that the last described catalyst was employed and the temperature in the reaction zone was 320 C. the yield of the purified azelonitrile from azelaic acid was There was no deterioration of the catalyst after 1000 hours of continuous operation, but on the contrary, the breaking strength thereof increased.

EXAMPLE 5 The catalyst was prepared by dissolving 3.5 parts of silica gel powder of 80 to mesh as in Example 4 and 3.5 parts of potassium hydroxide in 100 pants of water. 8 parts of ammonium metavanadate were then added and the solution boiled with the evolution of ammonia, the resulti-ng solution having a pH of 7.0. 96.8 parts of the above silica gel powder were mixed with the solution and the procedure of Example 4 followed to complete the catalyst which had a breaking strength substantially that of the catalyst of Example 4. Employing the operating conditions of Example 1 except as set forth below the dinitrile of azelaic acid was produced at a 91.0% yield, and

The yield did not diminish even after 1000 hours of continuous operation.

It is apparent from the above that a very high overall yield is obtained in the production of aliphatic dinitriles from aliphatic dibasic acids. There is little loss in the vaporizing stage since the unvaporized acid is cooled and returned to the melter thereby minimizing polymerization or other undesirable modifications of the aliphatic dibasic acid. Furthermore the conversion efficiency in the reaction zone with the subject catalysts is high whereby to provide a high aggregate yield. Another important advantage is the long life of the vaporizing zone and reaction zone requiring a minimum of shutdown. It should be noted that the present process is particularly applicable to the dinitrilization of azelaic, adipic and suberic acids which may be employed in any of the examples.

While there have been described and illustrated preferred embodiments of the present invention it is apparent that numerous alterations, omissions and addition may be made Without departing from the spirit thereof.

What is claimed is:

1. In a method of producing an aliphatic dinitrile from the corresponding aliphatic dibasic acid and ammonia in the presence of a catalyst involving the steps of heating a dibasic acid selected from the group consisting of azelaic, adipic and suberic in a melting zone to liquify the dibasic acid, feeding said melted dibasic acid to a vaporizing zone, feeding ammonia to said vaporizing zone with said dibasic acid at a temperature above the vaporization temperature of said dibasic acid to vaporize said dibasic acid, feeding the vaporized dibasic acid and ammonia to a reaction zone containing a catalyst selected from the group consisting of mixtures of molybdic acid and phosphoric acid and mixtures of vanadic acid and phosphoric acid to effect dinitn'lization of the dibasic acid vapor in the presence of the catalyst, the improvement comprising vaporizing a portion of said dibasic acid at a temperature of from 320 to 350 C. in the vaporizing zone to form said gaseous mixture with ammonia, removing unvaporized dibasic acid from said vaporizing zone, cooling said removed dibasic acid, and recycling said unvaporized dibasic acid from said vaporizing zone to said melter.

References Cited in the file of this patent UNITED STATES PATENTS 2,132,849 Greenewalt et al Oct. 11, 1938 2,144,340 Lazier Jan. 17, 1939 2,273,633 Fluchaire et al Feb. 17, 1942 2,414,393 Potts Jan. 14, 1947 2,955,130 Guyer et a1 Oct. 4, 1960 FOREIGN PATENTS 822,531 Great Britain Oct. 28, 1959 OTHER REFERENCES Jordan: Vapor Pressure of Organic Compounds, 1954, pages 124 and 131. 

1. IN A METHOD OF PRODUCING AN ALIPHATIC DINITRILE FROM THE CORRESPONDING ALIPHATIC DIBASIC ACID AND AMMONIA IN THE PRESENCE OF A CATALYST INVOLVING THE STEPS OF HEATING A DISBASIC ACID SELECTED FROM THE GROUP CONSISTING OF AZELAIC, ADIPIC AND SUBERIC IN A MELTING ZONE TO LIQUIFY THE DIBASIC ACID, FEEDING SAID MELTED DIBASIC ACID TO A VAPORIZING ZONE, FEEDING AMMONIA TO SAID VAPORIZING ZONE WITH SAID DIBASIC ACID AT A TEMPERATURE ABOVE THE VAPORIZATION TEMPERATURE OF SAID DIBASIC ACID TO VAPORIZE SAID DIBASIC ACID, FEEDING THE VAPORIZED DIBASIC ACID AND AMMONIA TO A REACTION ZONE CONTAINING A CATALYST SELECTED FROM THE GROUP CONSISTING OF MIXTURES OF MOLBDIC ACID AND PHOSPHORIC ACID AND MIXTURES OF VANADIC ACID AND PHOSPHORIC ACID TO EFFECT DINITRILIZATION OF THE DIBASIC ACID VAPOR IN THE PRESENCE OF THE CATALYST THE IMPROVEMENT COMPRISING VAPORIZING A PORTION OF SAID DIBASIC ACID AT A TEMPERATURE OF FROM 320 TO 350*C. IN THE VAPORIZING ZONE TO FORM SAID GASEOUS MIXTURE WITH AMMONIA, REMOVING UNVAPORIZED DIBASIC ACID FROM SAID VAPORIZING ZONE, COOLING SAID REMOVED DIBASIC ACID, AND RECYCLING SAID UNVAPORIZED DIBASIC ACID FROM SAID VAPORIZING ZONE TO SAID MELTER. 